1. Field of the Invention
The present invention relates to wireless integrated circuit (IC) devices, and more particularly to a wireless IC device used in a radio frequency identification (RFID) system, and relates to a method of manufacturing the wireless IC device.
2. Description of the Related Art
In recent years, as a system for managing item information, a radio frequency identification (RFID) system in which a reader-writer that generates an induction field and a radio frequency identification (RFID) tag (also referred to as a wireless integrated circuit (IC) device) that is attached to an item, communicate with each other in a non-contact manner using an electromagnetic field and transmit predetermined information to each other has been put to practical use. Such an RFID tag stores predetermined information and includes a wireless integrated circuit (IC) chip that processes a predetermined radio signal and an antenna (a radiator) that performs sending/receiving of a high-frequency signal. Such RFID tags are used by being attached to various items to be managed (or packaging materials of the items to be managed).
As the RFID system, a high frequency (HF) band RFID system using a bandwidth of 13 MHz and an ultra-high frequency (UHF) band RFID system using a bandwidth of 900 MHz are common. In particular, the UHF band RFID system has a relatively long communication range and can collectively read a plurality of tags, and thus, the UHF band RFID system has been considered promising as an item management system.
In recent years, the RFID system has been applied in the medical field. For example, in Japanese Unexamined Patent Application Publication Nos. 2002-355258, 2004-121412, and 2011-015395, attaching a tag for a UHF band to a piece of surgical gauze has been proposed in order to prevent an accident such as leaving such a piece of gauze in the body of a patient by attaching a tag for a UHF band to such a piece of gauze and detecting the tag using a reader-writer.
In the medical field, an RFID tag that is attached to a piece of surgical gauze is often used in a liquid or in a high-humidity environment. In such environments, in the case where an antenna is exposed on a surface of an RFID tag, problems occur in that the antenna becomes corroded, and that structural components of the antenna are dissolved in the liquid. Therefore, in order to enhance environmental resistance characteristics of the antenna, the antenna needs to be coated with a resist material (a coverlay).
In other words, as illustrated in FIG. 16A, it may be considered that a resist layer 220 is provided on a pair of radiation portions 231A and 231B provided on a rectangular base material sheet 210 and extending in a long-side direction A from a center portion of the base material sheet 210, openings at which connection portions 232A and 232B of the radiation portions 231A and 231B (see FIGS. 16A to 16C, FIG. 17A, and FIG. 17B) are exposed are formed in the resist layer 220, the openings are filled with solder 228 (see FIG. 17C, and FIG. 17D), and a wireless integrated circuit (IC) element 250 is electrically connected to the solder 228. However, when the solder 228 is caused to melt due to reflow soldering used to make the electrical connection, the solder 228 is pressed by the wireless IC element 250, and the solder 228 in a molten state comes into contact with the resist layer 220. In this case, when an excessive amount of the solder 228 has been supplied, as illustrated in FIG. 17E and FIG. 17F, the solder 228 overflows the periphery of the wireless IC element 250, and ball-shaped solder grains 228a may sometimes be formed. In the case where printing misalignment occurs when the resist layer 220 is formed (printed), positions of the connection portions 232A and 232B are displaced. When such a problem occurs, electrical characteristics of the wireless IC element 250 vary resulting in, for example, mismatching of characteristic impedance.